
I can confirm that is nothing to do with the ECT sensor or more correctly the ECT sensor plug which is a three pin grey plug the cable colours being green/blue, pink/white & green/orange.
The only stock red cable on the CBF1000 runs from the battery to the ignition switch via the starter relay switch and regulator rectifier and that is certainly not part of that run. It will be an aftermarket extension to the loom probably to power some accessory that was previously mounted around the handlebar such as heated grips or a Sat Nav etc.
Your best friend here will be a multimeter, is it always 12v, switched 12v or 0v?
I'd check the battery terminals for an additional pair of black & red cables or under the seats for any loom extensions.